A homogeneous grey picture and a 'Mondrian' type of picture were illuminated by a projector with square-wave gratings of thirty different contrast values used as slides. Ten observers reported whether the picture appeared three-dimensional (3-D) (pleated) or flat. 3-D responses in this situation indicate colour constancy 'at the cost of' nonveridical depth perception. The frequencies of 3-D responses were significantly higher for the structured picture than for the homogeneous grey one. In reports of the direction from which the apparent 3-D object appeared to be illuminated there was a significant preference for responses "from above" when the grating was horizontally oriented. With vertical orientation there was no preference for "from the left" or "from the right". The results from the first experiment contradict traditional cue theories of depth perception since the projection of the borders between the fields of the structured picture was invariant and expected to inform about the flatness of the picture. They are, however, in line with a model for perceptual analysis of reflected light into common and relative components proposed earlier by Bergström. The difference in perceived direction of illumination between horizontally and vertically orientated gratings is discussed in connection with human ecology.
To what degree are young infants able to perceive differential shadowing and to what degree are they able to utilize this stimulus parameter as information about depth? Two habituation experiments were performed. In Experiment 1, a group of 5-month-old infants were habituated to a low frequency, vertical, and approximately sinusoidal luminance grating superimposed on a flat colored surface. This display induced stable 3-D perception in adult subjects. After habituation, the infants viewed two test displays at alternating trials. One was made up of real half cylinders matching the light distribution of the habituation display and the other was made up of a square wave grating of the same spatial frequency as in the habituation one. Adults perceived the latter display as flat. Results showed that both test displays were treated as new ones by the infants habituated to the sinusoidal grating. Experiment 2 was identical to Experiment 1, except that the subjects were 3 1/2-month-old. These infants treated the half cylinders as familiar and the square wave grating as new. The results indicate that infants at both age levels (3 1/2 and 5 months of age) were sensitive to the difference between sharp and gradual change in luminance which is a prerequisite for perceiving form from luminance. However, neither age group seemed to utilize gradual change in luminance as information about space.
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